New DPC Look-Up Table Methods for Three-Level AC/DC Converter

This paper presents new look-up table methods for a three-level ac/dc converter supplied from the grid. The nonlinear direct power control (DPC) method, by reason of its drawbacks resulting from the omission of grid inductance voltage drop, has been improved in the DPC-delta 5 x 2 method by rotating the orientation of coordinates by angle delta, i.e., the angle between grid voltage vector and set converter voltage vector. The other proposed development involves further improvement of the DPC-delta 5 x 2, into which a new optimal division of the current error plane is introduced. The new optimal voltage vector assignment allows us to choose a converter voltage vector using the modified error current vector. The proposed look-up table methods have been tested and compared applying the following criteria: current error, total harmonic distortion (THD) of input current, average transistor switching frequency, and response time on step changes of set current. The experimental results validate the proposed control schemes and show good system performances that were verified according to above criteria.